The lipase-catalyzed asymmetric C-C Michael addition

Article abstract of DOI:10.1016/j.molcatb.2010.11.011

The example of enzyme-catalyzed asymmetric C-C Michael addition was observed using Lipozyme TLIM (immobilized lipase from Thermomyces lanuginosus) in organic medium in the presence of water. This biocatalysis is applicable to the Michael additions of a wi

Full text of DOI:10.1016/j.molcatb.2010.11.011

Journal of Molecular Catalysis B: Enzymatic 68 (2011) 240–244
Contents lists available at ScienceDirect
Journal of Molecular Catalysis B: Enzymatic
journal homepage: www.elsevier.com/locate/molcatb
The lipase-catalyzed asymmetric C–C Michael addition
Jian-Feng Cai, Zhi Guan, Yan-Hong He∗
School of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The example of enzyme-catalyzed asymmetric C–C Michael addition was observed using Lipozyme TLIM
(immobilized lipase from Thermomyces lanuginosus) in organic medium in the presence of water. This
biocatalysis is applicable to the Michael additions of a wide range of 1,3-dicarbonyl compounds and
cyclohexanone to aromatic and heteroaromatic nitroolefins and cyclohexenone. The enantioselectivities
up to 83% ee and yields up to 90% were achieved. The enzyme can be reused for three cycles.
© 2010 Elsevier B.V. All rights reserved.
Received 10 August 2010
Received in revised form
20 November 2010
Accepted 20 November 2010
Available online 26 November 2010
Keywords:
Enzyme catalysis
Asymmetric C–C Michael addition
Lipase
1. Introduction
was demonstrated by the control experiments. This asymmetric
Michael addition activity of Lipozyme TLIM provided a novel case
C–C bond forming reactions are one of the mainstays of organic
chemistry. In this field the Michael reaction has numerous appli-
cations in synthetic chemistry [1–5]. The Michael reactions were
classically catalyzed by bases or suitable combinations of amines
and carboxylic or Lewis acids under homogeneous conditions. The
employment of these bases in the reactions encounters environ-
mental problems [6]. Therefore, there has been increasing attention
on the design and use of environmentally compatible catalysts [6].
On the other hand, biocatalysis has received great attention
as an efficient and green tool for the synthesis of pharmaceuti-
cal, industrial and agricultural chemicals and intermediates [7–10].
Some elegant works on enzyme-catalyzed Michael addition have
been reported, for example lipase catalyzed formation of C–C
[11–14], C–N [15–27], C–O [15], C–S [15,26,27] and d-aminoacylase
catalyzed formation of C–C bond via Michael addition [14,28].
However, to the best of our knowledge, enzyme-catalyzed asym-
metric C–C Michael addition has never been reported. Although
some efforts have been made by other groups [12–14,29], no
enantioselectivity has been observed in this biotransformation.
Herein, we wish to report the first discovery that Lipozyme TLIM
(immobilized lipase from Thermomyces lanuginosus) can catalyze
asymmetric C–C Michael addition in organic medium in the pres-
ence of water, and the enantioselectivities up to 83% ee and yields
up to 90% were achieved. The effects of organic solvent, temper-
ature and water content on the enzymatic Michael addition were
evaluated in detail. The catalytic specificity of immobilized lipase
of unnatural activities of existing enzymes.
2. Experimental
2.1. Materials
Lipozyme TLIM (immobilized lipase from Thermomyces lanug-
inosus, EC 3.1.1.3, 0.25 U/mg) was purchased from Novozymes
Biotechnology Co., Ltd. (Tianjin, PR China). Lipase from porcine pan-
creas (≥3000 U/mg enzyme activity pH 7.7, 37 ◦C) was purchased
from Shanghai Lanji Technology Development Co., Ltd. (Shang-
hai, PR China). Lipase from Candida cylindracea (4.28 U/mg), lipase
from porcine pancreas type II (100–400 U/mg protein, one unit
will hydrolyze 1.0 microequivalent of fatty acid from triacetin in
1 h at pH 7.4 at 37 ◦C) and Amano lipase M from Mucor javanicus
(≥10,000 U/g enzyme activity, pH 7.0, 40 ◦C) were purchased from
Sigma-Aldrich Trading Co., Ltd. (Shanghai, PR China). Lipase AYS
“Amano” Candida rugosa (≥30,000 U/g enzyme activity, one unit
is the amount of enzyme that releases 1 ␮mol of fatty acid per
1 min at pH 7.0), Lipase PS “Amano” SD from Burkholderia cepacia
(≥23,000 U/g enzyme activity, pH 7.0–8.0) and Lipase AK “Amano”,
from Pseudomonas fluorescens (≥20,000 U/g enzyme activity, pH
8.0, 60 ◦C) were a gift from Amano Enzyme Inc. (Shanghai, PR
China). Unless otherwise noted, all reagents were obtained from
commercial suppliers and were used without further purification.
2.2. Analytical methods
∗
All reactions were monitored by thin-layer chromatogra-
phy (TLC) with Haiyang GF254 silica gel plates. Flash column
Corresponding author. Fax: +86 23 68254091.
E-mail address: heyh@swu.edu.cn (Y.-H. He).
1381-1177/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcatb.2010.11.011

J.-F. Cai et al. / Journal of Molecular Catalysis B: Enzymatic 68 (2011) 240–244
241
Table 1
chromatography was carried out using 100–200 mesh silica gel
Enzyme screening for Michael addition of cyclohexenone and acetylacetonea.
at increased pressure. The 1H NMR spectra were recorded with
TMS as internal standard on a Bruker AMX-300MHz spectrometer.
Chemical shifts were expressed in ppm and coupling constants
(J) in Hz. HPLC was carried out using Chiralcel AD-H, OD-H, AS-H
columns. All the known products were characterized by comparing
the 1H NMR with those reported in the literature.
.
Yield (%)b
78
ee (%)c
2.3. Typical procedure for the enzyme catalyzed Michael addition
(synthesis of product a)
Entry
1
Enzyme
Time (h)
75
Lipase from
4 (S)
porcine pancreas
Lipozyme TLIM
Lipase from
Candida cylindracea
Lipase from
porcine pancreas
type II
Lipase AYS
“Amano” Candida
rugosa
Lipase PS “Amano”
SD from
Burkholderia
cepacia
Amano lipase AK,
from Pseudomonas
fluorescens
A mixture of ␤-nitrostyrene (3.0 mmol), ethyl acetoacetate
(1.0 mmol), Lipozyme TLIM (200 mg) in DMSO (5 ml) and deion-
ized water (0.5 ml) was stirred for 75 h at 35◦C. Enzyme was filtered
off to stop the reaction. CH2Cl2 was used to wash the filter paper
to assure that products obtained were all dissolved in the filtrate.
Then 30 ml of water was added to the filtrate, and the filtrate
was extracted with CH2Cl2. The organic phase was dried over
anhydrous Na2SO4, and the solvents were removed under reduced
pressure. The mixture was purified by flash chromatography using
EtOAc/petroleum ether (1:6 v/v) as eluent to afford the product a
as a white solid, 220 mg (79%, 65:35 dr, 16%/>99% ee).
2
3
75
75
75
63
17 (S)
11 (S)
4
5
6
75
90
90
50
22
13
5 (S)
5 (S)
7 (S)
7
8
90
90
35
34
2 (S)
0
2.4. The procedure for recycling and reusing of Lipozyme TLIM
Amano lipase M,
from Mucor
javanicus
A mixture of Lipozyme TLIM (200 mg), DMSO (5 ml), thienyl
nitroolefin (3.0 mmol), acetylacetone (1.0 mmol) and deionized
H2O (0.5 ml) was stirred at 35◦C. The same procedure as described
above was applied to obtain the product. The enzyme was recov-
ered by filtrating from the reaction system, washed twice with
ethanol and three times with acetone, and dried in the air at r.t. The
recovered enzyme was then used in the subsequent Michael reac-
tion without adding any new enzyme for the same stoichiometry
of substrates as that in the first cycle.
a
The reaction was conducted using acetylacetone (100 mg, 1.0 mmol), enzyme
(400 mg) cyclohexenone (194 mg, 2.0 mmol), deionized water (1 ml) and DMSO
(5 ml) at 60 ◦C.
Yield of the isolated product after chromatography on silica gel.
Enantiomeric excess and absolute configuration were determined by HPLC anal-
ysis using a chiral column [42].
b
c
3. Results and discussion
Table 2
Based on the concept that in organic solvents, enzymes acquire
remarkable properties such as enhanced stability, altered substrate
and enantiomeric specificities, molecular memory, and the abil-
ity to catalyze unusual reactions which are impossible in aqueous
media [30], we committed ourselves to screening of new activities
of existing enzymes in organic solvents. In our initial study, a pre-
liminary enzyme screen was performed (Table 1) to find out the
efficient catalyst for C–C Michael addition. The reaction between
cyclohexenone and acetylacetone was used as a model reaction,
and eight lipases were examined. As shown in Table 1, the best yield
of 78% was achieved using lipase from porcine pancreas, but it gave
inferior enantioselectivity with 4% ee (Table 1, entry 1). The good
yield of 75% with the best ee of 17% was obtained using Lipozyme
TLIM (Table 1, entry 2). In addition, the other tested lipases also
showed different degrees of catalytic activity, however, no better
enantioselectivity was obtained (Table 1, entries 3–8). Therefore,
we decided to investigate Lipozyme TLIM in Michael addition with
respect to the synthetic potential and stereochemistry of the prod-
ucts.
Having established the optimal catalyst, the solvent screen was
performed (Table 2) to find out the optimal solvent for this biotrans-
formation. The reaction in THF gave the best yield of 74%, while the
yields of 69% and 68% were obtained respectively in DMSO and DMF
(Table 2, entries 1–3). The other tested solvents gave lower yields
(Table 2, entries 4–10). No clear correlation between solvent polar-
ity and the enzyme activity was observed. We also investigated the
enantioselectivity of this enzymatic reaction in different solvents,
and the best ee value of 17% was obtained from DMSO. Interest-
ingly, we found that enzyme enantioselectivity in organic media
Michael reaction of cyclohexenone and acetylacetone catalyzed by Lipozyme TLIM
in different solventsa.
.
Entry
Solvent
Time (h)
Yield (%)b
ee (%)c
1
2
3
4
5
6
7
8
THF
DMSO
DMF
EtOH
H2O
1,4-Dioxane
n-Hexane
48
48
48
48
48
48
48
48
48
48
75
84
74
69
68
56
55
45
38
32
5 (R)
17 (S)
5 (S)
7 (R)
2 (S)
8 (R)
7 (S)
4 (R)
2 (R)
11 (S)
Toluene
9
Ethylethere
Acetonitrile
DMSO (no enzyme)
DMSO (Lipozyme TLIM
inhibited with PMSFf)
20
19
10
11
12
n.d.d
n.d.d
a
All reactions were carried out using acetylacetone (100 mg, 1.0 mmol), Lipozyme
TLIM (400 mg) cyclohexenone (194 mg, 2.0 mmol), deionized water (1 ml) and
organic solvent (5 ml) at 60 ◦C.
b
Yield of the isolated product after chromatography on silica gel.
Enantiomeric excess and absolute configuration were determined by HPLC anal-
c
ysis using a chiral column [42].
d
e
f
n.d.: Not detected.
Under reflux.
Pre-treated with PMSF (phenylmethanesulfonyl fluoride) at 25 ◦C for 24 h.

242
J.-F. Cai et al. / Journal of Molecular Catalysis B: Enzymatic 68 (2011) 240–244
Table 3
Investigation of substrate scope in Lipozyme TLIM catalyzed Michael additiona.
Entry
Acceptor
Donor
Product
a
Time (h)
75
Yield (%)b
79
drc
ee (%)d (config.)e
16/>99f
1
65:35
2
3
b
c
72
70
53
90
9 (S)
60:40
n.d.g
4
5
6
d
e
f
72
72
72
30
75
45
8 (R)
52 (R)
7 (S)
7
g
72
65
60:40
n.d.g
8
9
h
i
72
72
50
56
8 (S)
3 (R)
10
j
110
60
84:16
7/25f
11
12
k
l
72
68
85
43f
83f
125
13
14
15
m
n
168
96
73
75
32
98:2
23/>99f
30 (S)
n.d.g
o
72
16
17
p
q
120
240
n.d.h,i
n.d.h
18
r
s
240
264
trace
n.d.h
19
a
The reaction was conducted using the donor (1.0 mmol), the acceptor (3.0 mmol), Lipozyme TLIM (200 mg), H2O (0.5 ml) and DMSO (5 ml) at 35 ◦C.
Yield of the isolated product after chromatography on silica gel.
b
c
d
e
f
Dr was determined by 1H NMR and HPLC analysis using a chiral column.
Enantiomeric excess was determined by HPLC analysis using a chiral column.
Absolute configuration was determined by comparing the retention time of HPLC of adduct with that of literature data [43–49].
Absolute configuration was not determined.
g
h
i
n.d. = Not determined.
n.d. = Not detected.
No Michael product was detected; only a Knoevenagel product was obtained.

J.-F. Cai et al. / Journal of Molecular Catalysis B: Enzymatic 68 (2011) 240–244
243
Table 4
Recycling and reuse of Lipozyme TLIMa.
.
Cycle
Time (h)
Yield (%)b
ee (%)c
83
62
5
1
2
3
4
120
120
120
120
85
70
52
18
0
a
Reaction conditions: Acetylacetone (1.0 mmol), thienyl nitroolefin (3.0 mmol), DMSO (5 ml), deionized H2O (0.5 ml), Lipozyme TLIM (200 mg for the first cycle) at 35 ◦C.
Yield of the isolated product after chromatography on silica gel.
ee was determined by HPLC analysis using a chiral column.
b
c
depends on the solvent, and even reversal of enzyme enantioselec-
To our great delight, the Lipozyme TLIM catalyzed Michael reac-
tion showed an enantioselectivity, and this was the first example
of enzyme catalyzed asymmetric C–C Michael addition. The reac-
tion between nitrostyrene and ethyl acetoacetate gave 16% ee for
the major diastereomer (Table 3, entry 1). The monosubstituted
nitrostyrenes only gave low ee values (Table 3, entries 3, 4, and
6–8), but disubstituted nitrostyrene 2,4-dicholo-␤-nitrostyrene
gave moderate of 52% ee with diethyl malonate (Table 3, entry 5)
probably due to the effect of steric hinderence on the induction
of the enantioselectivity. Notably, the good enantioselectivity of
83% ee was obtained between thienyl nitroolefin and acetylace-
tone (Table 3, entry 12). Besides, thienyl nitroolefin gave 43% ee
with diethyl malonate (Table 3, entry 11), and 23% ee for the major
diastereomer with cyclohexanone (Table 3, entry 13). However,
furyl nitroolefin only gave poor enantioselectivities when reacting
with diethyl malonate and cyclohexanone (Table 3, entries 9 and
10). Furthermore, cyclohexenone gave 30% ee with acetylacetone
(Table 3, entry 14). Finally, when ethyl acetoacetate and cyclohex-
anone were used as the Michael donors, the products were obtained
with moderate to excellent diastereomeric selectivities (dr values
of 60:40–98:2) (Table 3, entries 1, 3, 7, 10, and 13).
Finally, we addressed the problem of enzyme recycling. At
the end of the reaction of thienyl nitroolefin and acetylacetone,
the enzyme was recovered by filtrating from the reaction sys-
tem, washed twice with ethanol and three times with acetone.
The enzyme was dried in the air at r.t., and reused in the next
cycle. The reaction was performed four times using same Lipozyme
TLIM without adding any new enzyme. The results are shown in
Table 4. The gradual decrease in activity and enantioselectivity was
observed for the first two cycles (Table 4, cycles 1 and 2). However,
the yield and ee dropped evidently at the following cycles (Table 4,
cycles 3 and 4). The decrease in yield upon repeated use was prob-
ably ascribable to a gradual deposition of tar compounds on the
catalyst surface which, after two cycles, began to hamper access of
the substrate to the catalytic sites. Furthermore the gradual denat-
uration of the enzyme may be the other causation. According to
the concept proposed by Klibanov and co-workers that the effect
of organic solvents on an enzyme is primarily due to interactions
with the enzyme-bound, essential layer of water rather than with
the enzyme itself [50], we think that the recycle process demolished
the prerequisite water layer around the catalyst particles, so it is
easy for the enzyme to interact with the organic solvents, causing
denaturation.
tivity upon a change in the solvent was observed (Table 2). There
have been numerous reports regarding this phenomenon [31–41];
however, in the most of them, no mechanistic explanation of the
observed behavior was offered. This observation may be attributed
to specific interactions between the solvent and the lipase. Based
on the results of solvent screen, DMSO was chosen as the optimum
solvent for the enzymatic Michael reaction. In addition, no product
was detected in the blank experiment (Table 2, entry 11). Besides,
it was experimentally verified that the inhibition of Lipozyme TLIM
caused a complete disruption of the catalytic activity of the enzyme
(Table 2, entry 12). The control experiments clearly indicated that
Lipozyme TLIM had a specific catalytic effect on Michael addition.
To further optimize experimental conditions, we examined the
effects of water content, temperature, molar ratio of substrates and
enzyme loading on the yield of Michael reaction. As a consequence,
0.1 water content (water/solvent, v/v), 35 ◦C, 3:1 (acceptor/donor)
and enzyme concentration of 36 mg/ml were chosen as the optimal
conditions.
To test the substrate generality of Lipozyme TLIM cat-
alyzed Michael addition, different aromatic and heteroaromatic
nitroalkenes, cyclohexenone, as well as other ␣,␤-unsaturated
aldehydes and ketones were used as the acceptors to react with 1,3-
dicarbonyl compounds and cyclohexanone under the optimized
conditions. The results were summarized in Table 3. It can be seen
that a wide range of substrates could participate in the reaction.
Both electron-donating and electron-withdrawing functionalities
were compatible (Table 3, entries 3–8). The best yield of 90% was
obtained for the reaction of 4-chloro-␤-nitrostyrene and ethyl ace-
toacetate (Table 3, entry 3). It was observed that ethyl acetoacetate
was more reactive than diethyl malonate as the Michael donor in
the enzymatic reaction, probably due to the easy formation of eno-
late. In addition, furyl nitroalkene reacted with diethyl malonate
as well as cyclohexanone to give the corresponding products in
acceptable yields (Table 3, entries 9 and 10). Thienyl nitroalkene
also gave good yields with diethyl malonate, acetylacetone and
cyclohexanone (Table 3, entries 11–13). Moreover, it is notewor-
thy that cyclohexenone was also successfully used as the acceptor
in this Michael reaction, and it gave a good yield of 75% with acety-
lacetone (Table 3, entry 14), and a low yield of 32% with diethyl
malonate (Table 3, entry 15). Next, we attempted to expand the
scope of acceptor to cinnamaldehyde, acrolein and benzalacetone.
It was observed that the reaction between cinnamaldehyde and
acetylacetone only gave a Knoevenagel product (Table 3, entry 16).
Meanwhile, only trace product was detected after 240 h for the
reaction of acrolein and cyclohexanone (Table 3, entry 18), but no
product was observed for the reaction of acrolein or benzalacetone
with ethyl acetoacetate (Table 3, entries 17 and 19).
4. Conclusion
In summary, we describe here the first enzyme catalyzed asym-
metric C–C Michael addition using Lipozyme TLIM as a recyclable

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J.-F. Cai et al. / Journal of Molecular Catalysis B: Enzymatic 68 (2011) 240–244
biocatalyst. The enantioselectivities up to 83% ee and yields up
to 90% were achieved. The reaction conditions including organic
solvents, water content, temperature, molar ratio of substrates
and enzyme loading were optimized. Lipozyme TLIM can catalyze
the biotransformation of a wide-range of substrates in DMSO in
the presence of water under mild reaction conditions. The spe-
cific catalytic effect of Lipozyme TLIM was demonstrated by the
control experiments. This asymmetric Michael addition activity of
Lipozyme TLIM provided a novel case of unnatural activities of
existing enzymes in organic medium, which is important for dis-
covery of new enzyme activities. Further studies focusing on the
improvement of enantioselectivity of this enzyme catalyzed asym-
metric transformation are currently under investigation.
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